1. Field of the Invention
The present invention relates to apparatuses for generating gases in drilled boreholes and methods of using these apparatuses. One of the apparatuses can be used to explosively fracture a vertical or horizontal deep drilled borehole below the water table and another of the apparatuses can be used to enhance the permeability of soil in the area or to generate remediation gases in contaminated soil adjacent to a vertical shallow drilled borehole above the water table.
2. Background Information
The production of oil and gas from geological reservoir formations in the earth is dependent upon the fluid permeability of those formations whereby the hydrocarbon liquid or gas can migrate into the producing wells to be recovered. In many reservoir formations, the natural permeability of the porous rock and/or the presence of natural tectonic fractures is sufficient to allow good production of the hydrocarbon liquid and/or gas. Other formations are known to contain the oil or gas in compartmentalized geological structures which are not interconnected and, hence, cannot be produced without drilling additional wells or otherwise disrupting the restraining compartments adjacent to existing wells. Still other formations are known to hold their oil or gas resource primarily in faults and fractures in otherwise low porosity rock formations and, hence, the producing drill hole must physically intercept these faults and fractures in order to recover the oil or gas.
In those cases where the drill hole fails to intercept the reservoir oil or gas storage compartment or fault or fracture zone, the geological materials surrounding the drill hole may be artificially fractured to facilitate fluid flow connections between the hydrocarbon storage zones and the drilled well. The most common technology used for this purpose is one of imposing a relatively high hydraulic pressure in the borehole, usually localized to the depth interval of interest by means of temporarily expandable plugs (packers), which will stress the rock sufficiently to overcome its tensile strength and thereby create fracture cracks which extend radially away from the wellbore axis. By driving the fracture fluid into these cracks, they can be made to grow and extend away from the wellbore and may intercept the oil and gas storage zones of interest. Residual tectonic stresses in the drilled formations have a primary influence on the direction and extent of the hydraulically induced fractures. This latter influence inhibits the ability to select and control the direction and number of fractures that may be created by the hydraulic fracturing process. As a consequence of the existing fracture structure relative to the position of the drilled borehole, the hydraulically induced fractures may or may not extend and intercept the oil or gas storage zone targets of interest.
Further, hydraulic fracturing is not effective in permeable ground where the fluid just dissipates into the ground and is not driven into the fracture cracks. Hydraulic fracturing also does not work well in horizontal wells in ground with many vertical faults because these faults allow the fluid and pressure to escape from the borehole.
Alternative methods of fracturing drilled geological formations have involved the use of solid or plastic explosive materials placed or tamped in the wellbore. The large amount of energy released in an explosive impulse tends to dominate the initiation of cracks in the borehole wall in a manner which can override the influences of the residual tectonic stresses in the formation. Therefore, with the use of these explosives, several induced fractures can be initiated in different directions to offset the directional disadvantage of hydraulic fracturing. The technical disadvantage of explosive fracturing is that the explosive impulse will tend to greatly overstress and to form rubble in the immediate borehole wall with the consequence that excessive energy is expended near the wellbore without useful results. Thus, the resulting fractures do not extend deeply into the formation surrounding the borehole. Moreover, the explosion-driven materials (e.g., gases and granular debris) that do penetrate the newly initiated cracks are not explosively active and, hence, have only a modest influence on the crack growth. Another very significant disadvantage of conventional explosive fracturing is the necessity of handling large amounts of hazardous explosive materials, either solids or gases, at the surface and in the borehole.
A fundamental approach to overcoming the hazards of handling explosive materials, either solid, liquid, or gaseous, is one in which the ingredients of the explosive material are inert when separated and may be combined and mixed at the final location where detonation is desired. Two-component liquid explosives and fuel and oxidant gaseous explosives are appropriate for use in this approach. However, mixing of the final explosive material becomes difficult in a downhole environment where accurate control and intermingling of the separate components is critical to achieving the desired explosive mixture. The optimum energy yield of the explosive reaction requires uniform mixing and stoichiometric composition of the reactive components, making the mixed process of any two-part composition a difficult control problem at the downhole pressure and temperature.
To overcome the various limitations cited above for the hydraulic and conventional explosive fracturing techniques in deep drilled boreholes, a new apparatus and method are needed to fracture these drilled boreholes. The use of the apparatus of the present invention, a gas generating electrolyzer, overcomes all of the problems with the known fracturing methods.
In addition to the use of the apparatus of the present invention in drilled boreholes below the water table, the apparatus can be used in drilled boreholes above the water table to loosen soil and thereby enhance the permeability of contaminated soil around the drilled borehole so that remediation processes will work more efficiently. Further, a modified configuration of this apparatus can be used to generate gases which can be used in a number of different remediation processes.
Environmental remediation processes such as in situ biodegradation via microorganisms, purging of volatile liquid contaminants or their vapors and gases by air sparging, drawing vapors and gases from the ground by vacuum, and either mobilizing or fixating contaminants by injecting solvents or other chemical reagents into the contaminated zone, are potentially effective in breaking down and removing, or arresting the migration of contaminants in soil and other permeable earth materials. The effectiveness of these processes depends upon the ability to introduce and distribute the remediation agent into the contaminated zone so as to promote the degradation or removal of the contaminant. How readily the contaminant enters the formation is dependent upon the porosity and permeability of the contaminated ground. If the porosity and permeability are low, an extended time period is required for the contaminant to diffuse away from its source. Remediation of such zones of contamination can be accelerated if the remediation agent, for example, a colony of biodegrading microorganisms appropriately selected to break down or consume the contaminant in situ, can be more easily introduced into the contaminated zone. A common and direct approach to facilitating such remediation access is to drill injection boreholes and return ventilation boreholes into the suspected subsurface contaminated zone so that the treatment mechanism can be placed in direct contact with the contaminant. However, even with this means of direct access, the diffusion of the remediation process is generally dependent upon the same natural permeability of the ground that permitted the original contaminant diffusion.
There is an important need to improve the effectiveness of such in situ remediation processes. There is also a need to improve the effectiveness of air sparging of contaminated soil. The apparatus of the present invention can effectively loosen the compaction or cementation of granular soil particles surrounding a soil borehole above the water table and thereby enhance the permeability of the contaminated zone of access around the borehole.
The use of prior art hydraulic fracturing techniques in shallow boreholes drilled in soil or other unconsolidated material would be of limited value since the static pressure needed to produce yielding stresses in the surrounding soil cannot generally be attained because of the existing natural permeability of most soils. The use of the prior art explosive fracturing techniques in soil boreholes is also of limited value because of the difficulty in controlling the localized stresses around the exploding charge which can cause excessive yield in the surrounding soil, resulting in local absorption of the impulsive overpressure needed to loosen the granular materials at larger radial distances away from the borehole. Further, both of these prior art methods introduce additive material into the soil. The explosive fracturing method requires specialized handling of the explosive materials and imposes potential safety hazards in its use.
The disclosed invention is a gaseous combustion technique that overcomes the disadvantages associated with the prior art hydraulic and explosive fracturing techniques described above.
The apparatus of the present invention can be used in similar methods to produce gases in drilled boreholes above and below the water table. Both methods provide advantages which include controllability of the combustion energy and the impulsive overpressure applied to the borehole wall, uniform distribution of the impulsive pressure along the borehole depth zone of interest, generation of only pure water as the combustion product after each reaction, and safe operation because no hazardous materials are handled.
Additional advantages of the method of using the apparatus of the present invention in deep drilled boreholes below the water table are introducing multiple fracture cracking into the borehole wall independently of residual stress directions in the formation and delivering active fracture growth forces to pre-existing and induced fractures of the borehole wall.
Additional advantages of the method of using the apparatus of the present invention in shallow drilled boreholes above the water table are providing repetitive impulsive pressurization of the borehole without requiring new or additional materials to be introduced into the borehole between each pressure impulse and permeating the pores of the soil with the gaseous combustion components to cause more effective loosening of the material upon combustion.